Conventional hydraulic closed circuit systems include those described in Japanese Patent Applications JP,A 58-57559 A (Patent Document 1) and JP-2001-2371-A (Patent Document 2).
JP,A 58-57559 A describes use of a flushing valve for controlling a surplus fluid flow developed in a hydraulic closed circuit including a single rod type hydraulic cylinder whose size of pressure-receiving areas differs between head and rod sides of the cylinder.
JP-2001-2371-A describes use of a flushing valve (equivalent to the flushing valve described in JP,A 58-57559 A) for avoiding a surplus and deficit of a fluid flow in a hydraulic closed circuit including a single rod type hydraulic cylinder having different size of pressure-receiving areas between head and rod sides of the cylinder. JP-2001-2371-A also describes use of disengaged pressure holding valves for obtaining stable actuator operation.